In order to improve power efficiency of wind turbine generators the aerodynamic properties of wind turbine blades may be adapted to wind conditions by adjusting the pitch of blades or otherwise modifying the shape of blades. In particular it may desirable to adjust or optimise the lift on blades. However, in order to adjust the lift properly, the angle and speed of the resulting air impinging on the blade should be known. The angle of the resulting air flow is commonly referred to as the angle of attack.
The angle of attack may be measured by pitot tubes arranged at the blade. However, the pitot tube protrudes out from the blade and affects the aerodynamics of the blade. The pitot tube may also be sensitive to dirt and other environmental exposures.
Accordingly, it would be desirable to have a sensor for determining the angle of attack which is robust enough to withstand the harsh environmental conditions which wind turbine generators are often exposed to. It would also be desirable to have a sensor which minimizes undesired effects on the aerodynamic properties of the wind turbine blades.
US 2008/0317598 discloses a wind turbine blade assembly which includes at least one local load sensor disposed on and/or within a surface of the wind turbine blade and at least one active flow modification device disposed on and/or within a surface of the wind turbine blade and configured to alter the aerodynamics of the wind turbine blade in response to real time local load sensor measurements such that a difference between a current angle of attack and an optimum angle of attack on the wind turbine blade is substantially minimized.
Whereas US 2008/0317598 discloses load sensors such as optical sensors for determining local blade loads and obtaining an angle of attack from the measured load, there is a need to find alternative methods and systems for determining the angle of attack.